A recent expansion of the historic St. Louis Art Museum by David Chipperfield Architects and HOK features a sophisticated daylighting system that fills the galleries with diffused natural light without adversely affecting the art on display. “It is so natural that you can feel a cloud go over head,” said HOK’s Roger McFarland. Designed with Arup, the system pipes in natural light through a coffered concrete ceiling, diffusing it throughout the galleries with a custom tool dubbed the “light spreader.”

The building’s 16-foot-high, 40,000-square-foot cast architectural concrete ceiling is divided into a grid of 680 rectangular coffers, each four feet deep. Centered above each coffer is a skylight made of double-glazed, low-iron glass. Light enters through the skylights and bounces off the concrete, which is infused with titanium dioxide to lend the material 55 percent reflectance—nearly twice that of typical concrete.

The field of skylights cannot be seen from outside. Adjoining the Cass Gilbert-designed “Palace of Fine Arts” constructed for the 1904 World’s Fair, the new East building does not trumpet its presence. Instead it is low and flat, in deference to its historic neighbor.

J.J. Lane; Alise O'Brien

Once light enters the skylights and bounces around among the reflective concrete, it meets the light spreaders, which are suspended within each coffer. The spreaders diffuse the daylight further, creating an even distribution of light throughout the space. The light spreaders were made by St. Louis-based fabrication studio Troco. They consist of two layers—a 3form plastic light-diffusing material and a micro-perforated Barrisol fabric layer underneath—held in a rectangular aluminum frame. Between the two layers is a void that traps sound, so it also serves as an acoustical panel. By varying the density of the fabric, the design team fine-tuned the amount of light and sound reduction necessary across the ceiling grid.

The light spreaders also conceal the addition’s mechanical systems, which are floated within the space between the coffers and the skylights. “So it acts as a light diffuser, the light fixture holder, the sprinkler containment portion, the acoustical panel, and the track to hold exit signs, speakers, security cameras, and motion detectors,” said McFarland. “It’s a work horse. It hides all of the stuff that you have to have in a museum.”

Alise O'Brien

To test the system, the design team made a full-scale, 20-by-30-foot mock-up of the gallery and ceiling grid, even drawing up Mondrianesque paintings to test the appearance of different colors under the diffused light. Even after the real thing was built, museum workers tested each surface with humidity and light meters for months before the space opened to the public.

The unique lighting system traps heat near the ceiling, which helped the new wing achieve a 29 percent reduction in energy use compared to a museum with conventional systems, helping it earn LEED Gold certification.

After viewing hours, the building’s automation system pulls shades over the skylights and the addition’s two floor-to-ceiling glass walls that look out over St. Louis’ Forest Park. A Hyperium software system tracks the movement of the sun throughout the day, fine-tuning with shade controllers manufactured by Lutron an assemblage of translucent and blackout shades to maintain a consistent level of light within the interior. The system also supplements the Midwestern daylight with fluorescent fixtures positioned above the ceiling coffers, which fill in for daylight during evening hours.